A humidity sensor may be applied to a variety of industries in the form of being used individually or together with sensors that obtain other kinds of information. The humidity sensor may be applied to logistics services, transport services and traffic network, etc., thereby enhancing services related thereto. Also, the humidity sensor may be applied to history management, production management, plant management and environment network construction of agriculture, fisheries, livestock industry, distribution industry and manufacturing industry and the like, and may be also applied to smart home, office network and building control and the like with the intention of making a residential space pleasant. The humidity sensor may be also used to deal with other hazardous industry environment.
For the purpose of incorporating the humidity sensor with the above-mentioned various services, research is being devoted to higher sensibility, miniaturization, a lower price and reliability. In terms of the structure of the humidity sensor, the humidity sensor is recently evolving from a ceramic sintering or thick film structure to a micro sensor structure that chiefly uses a micro-electro-mechanical system technology to which a semiconductor process technology has been applied.
A humidity sensor's measurement method using a humidity sensing film is now the most widely used. The measurement method is to measure the electrical characteristics at a point of time when moisture is absorbed in or desorbed from the humidity sensing film composed generally of organic matter like polymer, etc., or inorganic matter like ceramic, etc. The measurement method is relatively simple. For example, the humidity is detected by the capacitance change or resistance change caused by the moisture absorption of the humidity sensing film. The humidity sensor using the above-mentioned humidity sensing film commonly uses a structure provided with only the humidity sensing film and sensing electrode.
However, regarding the conventional humidity sensor using the above-mentioned humidity sensing film, in a case where defects occur in manufacturing the humidity sensing film, a signal may be distorted due to the influence of a parasitic capacitance. Moreover, since the polymer layer should absorb the moisture, the reaction rate is low. Additionally, much time is required for detecting rapid change of the humidity. Also, the polymer is vulnerable to organic solvent like alcohol, etc., and may have a problem in adhering to electrodes. Besides, it is difficult to obtain stable characteristics under high temperature and high humidity conditions.
Therefore, there is a requirement for development of a humidity sensor capable of rapidly and accurately detecting humidity and of being applied to any medium.